Dry acid cleaning compositions



No Drawing. Filed Feb. 19, 1958, Ser. No. 716,052 6 Claims. (Cl. 252-87) The present invention is concerned with dry acid cleaning compositions. More specifically, it is concerned with the use of these compositions in the cleaning of water-home deposits from surfaces which are normally in contact with water.

Mechanical conditions, unusual operations, poor control and other similar conditions render water treatment not always completely efiective in preventing deposit formation on surfaces which are normally in contact with water. It is common practice to remove scale from such equipment as heat exchangers, boilers, evaporators, air conditioning systems, and various types of equipment by using mineral acids such as hydrochloric acid. Such cleaning procedures have proven themselves to be satisfactory insofar as deposit removal is concerned but, from the standpoint of safety and convenience, hydrochloric acid has the disadvantage of being hazardous to men and equipment, and causing material damage in some cases. Due to the hazardous nature of hydrochloric acid, acid cleaning is usually done by specialized service companies, which means substantial costs are incurred.

Recently there has been a trend in many industrial plants to conduct acid cleaning operations using dry acid formulations. Usually these a 'd leaners consist of either citric acidWic acid and the like- These anmtssfllf. safatmusaandha ifililflfifisitakls s ra a iahibiwr, they w fill'lm tf y damagifi'g'metal surfaces. These dry acids, when used alone, are 'rela'tively sel 'tive as to the type of deposit they act upon. Thus, while performing satisfactorily in cleaning certain types of specific scales, they oftentimes will lease residues of deposit where the composition of the deposit is composed of a blend of two or more types of scale constituents.

It would be of benefit to the art if a dry acid cleaner were available which would operate on a variety of deposits to completely remove such deposits from numerous types of surfaces. It would also be beneficial if a noncorrosive dry acid cleaning formulation or product were evolved which would be free from the several disadvantages now occasioned by the use of dry acid type cleaners. It, therefore, becomes an object of the invention to provide a new dry acid type cleaner which will act upon a variety of deposits and which may be used without the attendant disadvantage of prior art dry acid cleaners.

Another object is to provide dry acid cleaners which are relatively non-corrosive to various types of metals under conditions of use. Other objects will appear hereinafter.

In accordance with the invention, it has been found that superior so I am e eamg on m n. y be obtainfi blending hydroxy substituted carboxylic acids with sulfamic acid to give a synergistically acting product which is superior to either of the individual in gredients when used alone as cleaning regenerants. The hydroxy substituted carboxylic acids contemplated within the scope of this invention are those acids which will dissolve in water at 20 C., as their calcium salts, to the extent of at least 500 parts per million. They may also be defined as having dissociation constants (K of from 2 l0 to l l- As a general rule, they will not contain more than carbon atoms in chain length. In a preferred embodiment of the invention, the weight REFERENCE ratio of the hydroxy substituted carboxylic acid to sulfamic acid will be about 1:15. Generally, the synergistic effects may be achieved by maintaining the weight ratio of hydroxy substituted carboxylic acid to sulfamic acid in a general range of 1:2 to 2:1.

The hydrox s stituted arb lic acis of the type descn include such acids as m c, taric, gluconic, lactic and salicylic. The preferred acids are those which are hydroxy substituted polycarboxylic acids, with the most outstanding acid of this group being citric acid. I While the synergistic blends of acids thus described i may be used alone in the practice of the invention, it is desirable to blend therewith a corrosion inhibitor in a proportion of aut 10 to I y wei t on the total weight of acids and inhibitor, to reduce the corrosive attack of these acids on various types of metals. The use of corrosi miphilggg gs fpg agggg types of ac i s is Well EuOWn. Thus, for instance, such inhibitors as s lum meta borate, ammonium thiocyanate, so rum silicate, borax, s i m nitrate, various phosphates and molecularly dehy i'sfi'msphates, of which sodium hexametaphosphate is exemplary, may be used. Alkali metal arseno borates, arsenites, and the like, also may be employed to inhibit the novel compositions described herein.

In a preferred embodiment of the invention it is desirable to use as an inhibitor from 1% to 5% by weight of a higher monoalkyl substituted quaternary ammonium base wherein the higher aliphatic group contains from 6 to as many as 23 carbon atoms in chain length. For purposes of illustrating this type of inhibitor, the following general formula is presented:

where R, R, R", and R'" may represent organic radicals which are predominantly hydrocarbon in nature and may i be either aliphatic, cyclo aliphatic, aromatic, aralkyl, 1 alkaryl and the like, and sub-combinations of R, R", I R', and R'"' may form a heterocyclic ring which may or may not contain such substituents as the elements, S, O, P and N. A- represents an anion, preferably inorganic, such as halide, sulfate, phosphate and the like.

Typical compounds coming within the scope of the general formula described above are such compounds as N-octyl pyridinium chloride; N-methyl, N-octadecyl, piperizinium sulfate; and octadecyl tn'methyl ammonium bromide, as well as other compounds of this general type.

A more specific and preferred type of higher alkyl sub stituted organic base comprises the well-known imidazolinium salts which are exemplified in the following US. patents: 2,267,965; 2,355,837; 2,738,325. For purposes I of completeness, the various imidazolinium salts described in these patents are incorporated herein by reference. A particularly useful imidazolinium salt for inhibiting the corrosive tendencies of the inhibitors is the compound 2-coco-l-(2-hydroxyethyl)-l-benzyl imidazolinium chloride.

In use, the compositions of the invention are made up into aqueous solutions which should generally contain from between 1% to 10% by weight of solids. Usually effectiveness can be achieved by using from between 1% and 5% by weight solutions. To treat most deposits, it is advantageous to heat the treating solutions to temperatures above normal room temperature (72i-5 F.), and to any temperature below the normal boiling point of water. Preferably temperatures ranging between 100 F. and 210 F. are employed.

The deposits upon which the compositions of the invention act most favorably are those inorganic deposits which are predominantly composed of one or more of the alkaline earth metal phosphates and carbonates, e.g., the calcium and magnesium compounds, and the several oxides of iron. Deposits of this nature, particularly when they are found on ferrous metal surfaces contacting water, are commonly referred to as scale. Scale removal is preferably conducted at a temperature in the range of 150 F. to 210 F.

Scales of the general types mentioned above are usually not uniform in composition but will often be composed of several components such as alkaline earth metal sulfates, various types of organic material and silica. While the compositions of the invention are not particularly suited to removing pure deposits of alkaline earth metal sulfates, pure organic substances or pure siliceous type scales, such constituents normally comprise less than one half of the deposit with the balance being carbonates, phosphates, oxides of iron and other metallic corrosion products. The cleaners selectively operate on the deposits of the latter class and, in so doing, will remove the other types which are present as an intimate admixture.

The cleaners are also effective in removing non-ferrous metal salts, such as copper oxide, or metallic copper deposits, which are frequently encountered on the ferrous metal surfaces of high pressure boilers.

The most frequent occurrences of scale or deposit formation are found on the metal surfaces of heat exchangers, low pressure boilers, pipelines, heat economizers, feedwater heaters, sterilizers, and the like. The surfaces of equipment of this nature commonly will be composed of ferrous metals and, in many instances, will be composed of the metals copper, aluminum, and admiralty metal, as well as various alloys of these metals. When inhibited formulations of the invention are used in contact with non-ferrous alloys, the corrosive attack is relatively mild as compared with the attack occasioned when such 'metals contact concentrated solutions of inhibited hydrochloric acid.

The invention has its most important application in cleaning metal surfaces contacted by scale, especially scale deposited in apparatus operated under heat exchanging conditions. It also finds application in cleaning other solid surfaces, such as, for example, sand filters, resinous ion exchange materials, acid resistant plastics, and the like, where deposit formation on these surfaces is a problem.

In certain types of cleaning problems superior results are obtained by first treating the contaminated surfaces with an alkaline material such as sodium hydroxide in the form of a dilute aqueous solution, e.g. 5%l0%. In the case of boilers and the like contaminated with large amounts of sulfate and silica type scales, the dilute alkaline solution is raised to an elevated temperature and then made to contact the scale for a period of time sufficient to loosen or dissolve the more tenacious type deposits encountered. The compositions of the invention are then made up into solutions where they are then used as an auxiliary treatment that removes the scale not aflected by the caustic preboil. They also act to neutralize any caustic material, which factor is important where such problems as caustic embrittlement occur.

A desirable incorporation into the formulas of the cleaning compositions is the addition of a minor amount of an indicator dye which will change color when the activity of the solution has been spent insofar as cleaning activity is concerned. Methyl violet, when used at concentrations of as low as 0.05% by weight of the total formula, gives superior results. A buffer may also be included, such as boric acid.

To ftn'ther illustrate the invention, the following typical cleaning formulas are presented:

Composition 1 Composition Vi Ingredient: Sulfamic acid Composition VII Ingredient: Citric acid 100 To illustrate the eflicacy of the formulas presented above, the following are given by way of example:

EXAMPLE I This example illustrates the cleaning of a scale-coated superheater section of a four-drum boiler.

Connections were made to both the saturated and dry superheater headers in order to circulate the cleaning solution. A vent line was installed on one of the headers and raised sufficiently high to give the proper heat pressure in order to fill all of the superheater elements. The superheater was filled with hot water, the temperature of which was about 160 F., and approximately pounds of Composition I was injected into the system by means of a small air pump, providing about a 2% aqueous solution of the composition.

After the solution of Composition I was injected into the system, the diluted solution was circulated for approximately four hours. The system was then drained, flushed with hot water and the headers were inspected. The headers were cleaned to bare metal.

EXAMPLE II This example illustrates the cleaning of a water well with the materials of the invention. Composition IV was made up into a 4% solution and was introduced into the discharge line of the pump where it was allowed to flow down through the pump casing to the water level. Once the chemical solution was in place, the pump was operated and the solution recirculated to a by-pass in the discharge line from which point it went back into the well annulus. Following this recirculation, the solution was circulated approximately ten times over a period of six to eight hours. This circulating alternately drew the water from the strata and then allowed it to flow back. This procedure indicated an excellent iob of removing the calcium carbonate deposits which were plugging the strata and which also surrounded the screen.

EXAMPLE III A triple effect evaporator which was operated in a large salt manufacturing plant was encrusted with large quantities of a scale which was predominantly composed of calcium sulfate. A solution of sodium hydroxide was fed into the tank and the temperature elevated to 200 F. for a period of four hours. At the end of this time, the treating solution was drained and an inspection indicated the scale to have been changed somewhat in its appearance, yet substantial amounts still clung tenaciously to the metal surfaces of the tank. Immediately following the caustic preboil, a 4% solution of Composition V was added to the unit. The temperature was elevated to about 190 F., and the treating solution remained in contact with the scale for about eight hours. At the end of this time, the treating solution containing Composition V was drained and an inspection revealed substantially all of the scale had been removed.

EXAMPLE IV A tank car which had been used to transport gasoline had become encrusted with various types of iron oxides. A 2% solution of Composition III was placed in the tank and allowed to remain in contact with the deposits for a period of 24 hours at approximately room temperature. The treating solution was then drained from the car and a rinse solution added. An inspection of the interior of the car showed the metal to be completely free of iron oxides. It is interesting to note that there were amounts of organic deposits encrusted in the iron oxides and these organic deposits were also removed.

EXAMPLE V Composition II was made up in a 5% solution and was fed into the cooling jacket of a nail manufacturing machine which had become encrusted with large amounts of calcium carbonate and calcium phosphate type deposits. The temperature of the solution was elevated to 175 F., and intimate contact of the scale with the solution was maintained for a period of twelve hours. At the end of this time, the system was drained, flushed with cold water, and then inspected. Results indicated the scale to be completely removed.

EXAMPLE VI This example demonstrates the comparative cleaning efficiency of the invention as opposed to sulfamic acid alone versus citric acid alone used under comparable cleaning conditions.

Two percent aqueous solutions of Compositions I, VI, and VII were made up into 350-ml. test baths in a Berzelius beaker and where heated to 160 F. Uniform rings were cut from a scaled pipe and were suspended from a glass hook. After four hours the specimens were oven dried and inspected to determine deposit removal. The scale consisted of 70% calcium carbonate and 30% calcium sulfate. Beneath the scale were large amounts of iron oxides. Composition VII showed little eflect in removing the scale, whereas Composition I completely removed both the scale and iron oxides. Composition VI removed about 50% of the scale, but did not affect the iron oxide.

The invention is hereby claimed as follows:

1. A solid, acid cleaning composition which comprises a blend of (A) a hydroxy substituted carboxylic acid, said acid being soluble in water at 20 C., as its calcium salt, to the extent of at least 500 parts per million and having a dissociation constant (K of from 2X10" to 1X10- and (B) sulfamic acid, the weight ratio of (A) to (B) being within the range of 1:2 to 2:1, said composition containing from 2% to 30% by weight of a corrosion inhibitor.

2. The composition of claim 1 where the hydroxy substituted carboxylic acid is citric acid.

3. A solid acid cleaning composition comprising:

4. The process for cleaning a metal surface normally in contact with water under heat exchanging conditions to remove a scale deposit therefrom which comprises contacting said deposit with an aqueous solution of a composition comprising a blend of (A) a hydroxy substituted carboxylic acid, said acid being soluble in water at 20 C., as its calcium salt, to the extent of at least 500 parts per million and having a dissociation constant (K of from 2x10- to 1X10- and (B) sulfamic acid, the weight ratio of (A) to (B) being within the range of 1:2 to 2:1.

5. The process of removing a scale deposit which has formed on a metal surface normally in contact with water and which includes at least one compound from the group consisting of alkaline earth metal carbonates and phosphates, and the oxides of iron, which comprises contacting said deposit with a 1% to 10% by weight aqueous solution of a composition comprising a blend of citric and sulfamic acids combined in a weight ratio of 1:2 to 2:1, at a temperature within the range of F.-210 F.

6. The process of removing a scale deposit which includes at least one compound from the group consisting of alkaline earth metal carbonates and phosphates, and the oxides of iron, from a surface which has been fouled with said deposit through contact with water, which comprises contacting said deposit with an aqueous solution of a blend of (A) a hydroxy substituted carboxylic acid, said acid being soluble in water at 20 C., as its calcium salt, to the extent of at least 500 parts per million and having a dissociation constant (K of from 2 l0 to 1 10- and (B) sulfamic acid, the weight ratio of (A) to (B) being within the range of 1:2 to 2:1, said composition containing from 2% to 30% by weight of a corrosion inhibitor.

References Cited in the file of this patent UNITED STATES PATENTS 1,334,092 Harmeling Mar. 16, 1920 1,890,214 Churchill Dec. 6, 1932 1,994,633 Boyd Mar. 19, 1935 2,116,034 McGaughey May 3, 1938 2,148,006 Arveson Feb. 21, 1939 2,164,142 Moore June 27, 1939 2,220,451 Hunt Nov. 5, 1940 2,225,294 Bolton Dec. 17, 1940 2,287,050 Miller June 23, 1942 2,316,219 Brown Apt. 13, 1943 2,326,837 Coleman Aug. 17, 1943 2,383,800 Johnson Aug. 28, 1945 2,465,987 Gorman Apr. 5, 1949 2,606,155 Hill Aug. 5, 1952 2,607,722 Kreml Aug. 19, 1952 2,674,523 McDonald Apr. 6, 1954 2,692,189 Ro Oct. 19, 1954 2,698,781 Meyer Ian. 4, 1955 2,847,384 Conklin et al. Aug. 12, 1958 2,904,414 Ostrander et a1. Sept. 15, 1959 FOREIGN PATENTS 408,859 Great Britain Apr. 19, 1934 440,564 Great Britain Dec. 20, 1935 

1. A SOLID, ACID CLEANING COMPOSITION WHICH COMPRISES A BLEND OF (A) A HYDROXY SUBSTITYUTED CARBOXYLIC ACID, SAID ACID BEING SOLUBLE IN WATER AT 20*C., AS ITS CALCIUM SALT, TO THE EXTENT OF AT LEAST 500 PARTS PER MILLION AND HAVING A DISSOCIATION CONSTANT (K1) OF FROM 2X10-3 TO 1X10-5, AND (B) SULFAMIC ACID, THE WEIGHT RATIO OF (A) TO (B) BEING WITHIN THE RANGE OF 1:2 TO 2:1, SAID COMPOSITION CONTAINING FROM 2% TO 30% BY WEIGHT OF A CORROSION INHIBITOR. 